Conventionally, there is known a wind turbine generator for generating power by using wind power as natural energy. In some cases, such a wind turbine generator is installed in a cold weather where the outside air temperature is as low as −40° C. In such a Cold weather, as the outside air temperature decreases, accordingly decreased are the temperatures of electric devices provided in a nacelle of the wind turbine generator. As a countermeasure, there is proposed a method of maintaining the electric devices in the nacelle at a predetermined temperature by using a heater or the like, thereby compensating the operations.    Patent Citation 1: Japanese Unexamined Patent Application, Publication No. 2003-288832